Optical discs of today may e.g. be a CD-ROM (Compact Disc Read Only Memory) disc, a CD-R (Recordable) disc, or a DVD (Digital Versatile Disc) for storing digital information. The discs may have different storing capacity and data transfer rates for transferring data to or reading data from the disc. Providing audio/video data for real time recording/reading requires a high data transfer rate.
One optical disc supporting real-time recording/reading of audio/video data is the Blu-ray disc. Using a short-wavelength blue-violet laser, the Blu-ray disc successfully minimizes its beam spot size by making the numerical aperture (NA) on a field lens that converges the laser 0.85. In addition, by using a disc structure with a 0.1 mm optical transmittance protection layer, the Blu-ray disc diminishes aberration caused by disc tilt. This also provides a better disc readout and an increased recording density. The tracking pitch of the Blu-ray disc is reduced to 0.32 μm, almost half that of a regular DVD, achieving up to 27 GB high-density recording on a single-sided disc.
Since the Blu-ray disc utilizes global standard MPEG-2 transport stream compression technology, it is highly compatible with digital broadcasting for real-time audio/video recording, and a wide range of contents can be recorded. It is possible for the Blu-ray disc to record digital high-definition broadcasting while maintaining high-quality and other data simultaneously with video data if they are received together.
To read/write digital data on an optical disc by a drag and drop functionality, it is preferred that physical defect management in the drive is provided. Thus, the optical disc has to have a dedicated area of the recordable area wherein defect management data may be provided.
The Blu-ray video real-time requirements, i.e. 36 Mb/s read/write and 800 ms seek, match the maximum read-write speed of the Blu-ray disc and device. However, the requirements are incompatible with defect management. This means that there is currently no room for the extra delay caused by defect management while playing or recording digital real-time Blu-Ray video data.
In the Blu-ray standard a disc is a single partition containing either a continuous area without defect management or an area with defect management. The standard also requires a certain file system: BDFS (Blu-Ray Disc File System). UDF (Universal Disc Format) is a file system for optical discs. BDFS cannot administer as many files as UDF can, which makes BDFS impractical for PC data use, in which tens of thousands of files on a 27 GB disc can be expected. BDFS is an integral part of the Blu-ray disc and is highly capable of storing data with real-time requirement. UDF, on the other hand, may be used on a Blu-Ray disc in the PC environment. UDF may be used with a Blu-ray disc in which defect management is switched on and can hold tens of thousands of files. The Blu-ray disc standard makes it impossible to have defect management switched on and use it for BDFS at the same time because the logical to physical relationship, i.e. the logical zero point, is at a different location of the disc, is different in the two cases. Thus, separate discs have to be provided in order to meet the conflicting requirements of reading/writing both digital data with support for defect management and read/write real-time audio/video data according to the Blu-ray standard.